NATURE Prawns, parasites and peregrine falcons

Peregrine falcons were seen flying in the Partry hills – perhaps a young pair seeking a territory for breeding.

Prawns, parasites and peregrine antics


Country Sights and sounds
John Shelley

No visit to the sea would be complete without finding something to take home for tea, so it was out with the shrimp net and into the water. To say it was cold would be an understatement! May and June have let us down, but there remains hope. Anyway, better too much rain than too much sun.
We found prawns hiding along the edges of rock pools at low tide.
‘Shrimps,’ said an interested onlooker.
‘Prawns,’ said I. No prawn of mine shall be called a shrimp. The title of ‘prawn’ is somehow more noble, and the primitive arts of hunting and trapping are involved in its capture. Shrimp, on the other hand, can be casually scooped up by the score from any sandy shallow. At least that is what the name implies.
Biologically there some differences. Shrimp have two pairs of claws while prawns have three. Examination under a microscope will reveal some variation in the manner of respiration. On toast, where such things really matter, a large shrimp is a prawn.
About one in five of our specimens had strange yellow-green, half-inch swellings behind the head, just inside the transparent shell, or carapace. I picked one off to see what it might be. It moved – not much, but very definitely. What could it be?
Back at home we checked the internet. Yes, there it was, a Bopyrid isopod, a parasite that specialises in dining from its living host, draining vital body juices to meet its needs. This is truly one bizarre creature. On first hatching from an egg it swims to the surface in search of one of the free-swimming plankton animals called copepods, upon which it will feed through its juvenile stage.
Approaching maturity, the Bopyrid heads for the bottom of the sea, where it will find one or other of the benthic or bottom-dwelling crustaceans, such as our prawns, and finds its way inside the shell where it has free access to soft flesh. Having set up home it loses its legs and develops into the adult stage. The first Bopyrid to enter the carapace of a prawn becomes an adult female. The second and subsequent arrivals become male and attach themselves directly to the female. The female feeds, grows quickly and soon starts to produce eggs. The males remain tiny and appear to have only one purpose – to fertilise the eggs of the female.
These strange little animals must surely make some kind of contribution to the greater scheme of things. Whatever the role of Bopyrids may be, they are positively unappetising. Our infested prawns would be cooked and fed to the chickens, which can turn them into eggs.
We made a half-hearted attempt to gather cockles, finding few. It is just as well, for there is no ‘R’ in the month of June. Summer is in fact the spawning time for most shellfish. Reproduction leaves them nowhere near their best. They need until September to fatten again, when we shall be glad to find them once more.
Away from the sea I took guests up to Dirkmore where they caught wild trout that might never have seen an anglers fly, handsome little fish of half a pound with silver-blue flanks and vermillion spots. The Dirks are as wild and as free as any fishery could be.
Situated high on the flanks of the Partry Hills, they are subject to the very best (or worst, according to the insulating qualities of ones jacket) of Irish weather. A hungry wind swirls down from the peaks to whistle through rocky crags before sweeping away across the open moor, creating huge, almost intoxicating imbalances in air pressure. Dark clouds drop over the cliffs to scatter showers from dense fog. Startling sunshine is suddenly too hot, too humid. Horseflies and midges love it here.
We were entertained by a pair of peregrine falcons, which swooped up and down the cliff face where we thought they might have their nest. There were no signs of it. No white streaks of guano down the rocks and no preference for any particular location on the part of the birds. They are not incubating eggs or feeding hatchlings. Perhaps they are a young pair establishing a territory and will start to breed next year.